Claire Forrest comes from wealth yet lives independently in a run-down apartment, supporting herself with part-time jobs like working at a burger joint. This self-reliance stems from her strained relationship with her father, who expelled her mother under unexplained circumstances. Claire fiercely protects her brother Randy, reacting with deep anger toward their father when Randy's business fails, unaware her father was in Europe investigating the betrayal behind its collapse.

Her racial background is ambiguous; both Claire and Randy possess darker skin tones than their father, suggesting potential bi-racial heritage. Initially rebellious and perceived as a delinquent, Claire frequently skips school and spends time primarily with her close friend Juan. Despite her aloof exterior, she demonstrates fierce loyalty to those she trusts.

After death and reanimation, Claire fights as one of the "Dead Girls" for the Animus organization in supernatural conflicts. She exhibits aggression and quick reactions in combat, often wielding a baseball bat against humanoid monsters during nightly battles where failure means permanent death. Over time, she builds stronger bonds with fellow reanimated girls—Kate, Rachel, and Rose—and gradually works toward reconciling familial tensions, striving to become more grounded.

In an alternate reality 300 years later, Claire experiences significant personality shifts. She adopts a highly fashionable demeanor and becomes adept at manipulating men, contrasting sharply with her original tomboyish independence. Immortal but devoid of memories from her first 17 years, she balances ordinary school life with vigilantism, operating alongside her companions as bounty hunters in a ruined world. The group remains drawn to the Red Garden on Roosevelt Island, seeking answers about their past. During this era, they encounter and confront adversaries like the android Louise and Edgar Mayer, reaffirming their commitment to wander the world together indefinitely.